The AM Forum

..HI FROM TIM..GOT MY APACHE UP ES RUNNING,ALL SEEMED OK..I PUT SOME .01 CAPS ACROSS THE 510pf CAPS,TO GET RID OF THE HIGHS,AND IT SOUNDS BETTER..BUT..I'M RECEIVING REPORTS THAT THE RIG IS TOO WIDE..SPLATTER UP 20KC FROM MY FREQ...I REPLACED THE MIKE WITH  HI-IMPEDANCE DYNAMIC,AND THE AUDIO SOUNDS FB..BUT,IT IS STILL SPLATTERING,ALTHOUGH NOT AS BAD. I REMOVED THE CLIPPER TUBE,THE OB2s FER SSB...ALL METER READING APPEAR CORRECT,BUT I WOULD LIKE SOME INPUT AS TO THIS PROBLEM..BTW,THE REPORTS OF SPLATTER ARE NOT FROM STATIONS CLOSE TO MY QTH...ANY IDEAS?...TIM....SK..

Hi Tim,

Sounds like you need to sweep the rig to determine what's going on in there. Take a good hard look at the waveform with a tone and it will probably show you the problem.

Here's two short articles I wrote on the subject. Just what you need to figure out what's happening...  Take these steps and report back here what you see.  It can be cured.

http://amfone.net/ECSound/K1JJ1.htm

http://amfone.net/ECSound/K1JJ2.htm

73,
Tom, K1JJ

Running AM without a scope is like going to work without pants.

Also remember that the "real" audio gain control is located behind the key jack. The front panel "gain" control actually should have been labeled "clipper gain" control. If you're running the Apache without the clipper tube, the adjustment of the front panel gain control will overload the stages after it very quickly, unless you readjust the audio gain control behind the key jack. A better solution would be to relocate the audio gain control function to a front panel control.

Pete said:
Hmmmm... I seem to remember that being just the opposite Pete. However, I haven't messed with my Apache in quite sometime. I did do the SCC/YGC mods on it and the audio turned out pretty good.
Tim, make sure you are using a non-amplified D-104. Believe me and others when we say the audio is dang good.

For a stock Apache, manual indicates that zero clipping is only a few degrees above zero position on the front panel control. A quarter turn of that pot will give you almost 20% of clipping. This pot is ahead of the clipper; the one behind the key jack (audio gain pot) is after the clipper.

Adding larger coupling caps, without any other changes in the circuitry, will only aggravate the audio when trying to just use the front panel “gain” pot to control the audio level. There are also numerous audio mods floating around for the Apache. I changed my “clipper” front panel pot to do the function of the pot behind the key jack. I then changed out the pot behind the key jack to one with a shaft that protruded through the key jack hole. Added some RC components and turned the pot into a tone control.

Tim if the stations reporting wide audio are from another country, meaning solid state, have them turn off the noise blanker and be certain they have their filtering set at 2.4 KC.  That noise blanker is a bear on received signals of the AM type.

Also the real audio is the one behind the key jack.  It needs to be set for proper modulation.

The mods I did bypassed the clipper completely and changed the speech amp to cathode bias. The mic input was satified with a HI-Z mic.

Tim, when I last heard you, you indicated that you turned the mod up to max, on the behind-the-key-jack pot.  That is dangerous, in that you WILL  have way to much modulation., particularly without a clipper.  You definitely need a scope. Mean while, look at your mod current and keep it at about 125 mils or thereabouts. (assuming your running your plate dip at 250 mils). 

I run my rig at 200 mils, get about 100W out, and have loads of audio. And I use a scope always, on AM.

As should everyone.  THere's no excuse for not using one when you can get an old buzzard scope, that will work FB for 160/75, at just about any hamfest for a couple of bucks.

73 John

.....I'M USING A SCOPE,AND THE PATTERN LOOKS GREAT..THAT POT BEHIND THE KEY JACK ISNT WIDE OPEN,WAY TOO MUCH AUDIO..WHEN I FIRST GOT THIS THING RUNNING,I COULD'NT MOVE THAT POT,WHICH WAS FROZEN,WIDE OPEN...IT'S OK NOW,BUT I AM PLANNING TO REPLACE IT...KEN,VE3MAW FONED ME LAST NIGHT,AND HE WAS MONITORING MY SIG ON HIS SCOPE...HE RELATES THAT I'M NOT WIDE...SO I'M A LITTLE PERPLEXED..IT MAY BE GUYS WITH NOISE BLANKERS ON,ETC,BUT I WANT TO BE SURE THAT THIS THING ISNT TOO WIDE...AS I SAID,ALL LOOKS FB ON MY SCOPE...SK..

The scope doesn't lie.  If it looks like the pattern as seen in the background decoration on this very forum, you're fine.  If there are flat tops, spaces where there's zero carrier, or high frequency artifacts you're sure to get splattering.

Take reports with a grain of salt, as few hams understand what real "splattering" is and what it sounds like.  Could be as simple as someone having the NB on or listening to you on the wrong sideband.

Although I suspect with that control cranked to the fire you probably were firing a few far and wide  ;D

Did you put an audio tone through and CAREFULLY study the sine wve from 100- 4,000 cycles?

I've had rigs that would look good with a casual view of my own voice peaks, but there were still splatter reports.  When I studied it with a tone I could see a slight bit of deformity in the cross over point. Also, could see the sine curve up was not perfectly straight, but slightly tlited. No way to see that under "busy" voice modulation. 

Another thing is that at the extreme highs, maybe you are running into distortion that causes "spitting".

There's so many subtle things that could cause it. Sweep that rig and let us know the departures from a perfect sine wave...  The waveform will not be perfect, but it's a matter of degree and opinion how much splatter is considered OK... ;D  ie, we ALL have some splatter, since no rig has perfect modulation transfer from audio to RF.  The fine tuning is the hardest part - getting the last 10% tricked out.

T

Hello Tim:  ;D It sounds nice today time to load it into the rack for sure --its time to start working on that Collins 20V you have in the garage.-- 73 from Jim